Cutting oil composition



Un ted es Pat n CUTTING OIL COMPOSITION Everett C. Hughes, Shaker Heights, Harrison M. Stine and Samuel M. Darling, Lyndhurst, and Chien-wei Liao, Cleveland, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application September 13, 1954, Serial No. 455,747

8 Claims. (Cl. 252-45) The present invention relates to a cutting oil concentrate, cutting oils containing such a concentrate and characterized by a unique combination of superior cutting ability and absence of the formation of disagreeable odors when in use, and to a method of making the concentrate.

Oils containing sulfur or sulfur compounds dissolved therein have been suggested heretofore as cutting oils. Such oils also frequently contain chlorine and a fat such as lard oil. It is believed that the sulfur, to be effective in improving the cutting ability of a cutting oil, must be.

in an active form, i. e., not bound to a carbon atom, which can react with metal being machined under the conditions existing at the point of contact between the tool and the machined metal. Heretofore, the amount of active sulfur which could beincorporated into an oil has been dependent largely upon the solubility of free sulfur in the oil and upon the amount of sulfur which can be chemically combined but not bound to a carbon atom.

A great many suggestions have been made hereto,- fore for increasing the active sulfur content of cutting oils. In some instances, these suggestions have resulted in oils having excellent cutting ability but poor odor characteristics and/ or stability. In other instances, they have resulted in oils of acceptable odor but of poor cutting ability. In still other instances the oils developed have been found to be too dark or opaque to permit adequate viewing of the work during a machining operation. Generally it has been found that some compromise must be made among odor, stability, optical density and cutting ability factors, the cutting ability being improved with an increase in sulfur content at the expense, however, of odor, stability and opacity.

The odor characteristics of a cutting oil are not necessarily apparent upon an examination of the oil as produced or supplied to a user. are developed only when the oil is used in machining operations. This is apparently due to the formation of odoriferous compounds under the conditions prevailing at the cutting tool. If the cutting oil develops an unpleasant or obnoxious odor during use, it makes no difference how good the oil is from the standpoint of cutting ability, i. e., the number of pieces that can be machined with a given tool, the wear on the tool and the surface finish of the metal being machined because machinists will refuse to work with it.

I Hydrocarbon polysulfides containing one or more alkyl or aryl radicals have been suggested as being suitable for In many instances, odorsitself rather than of a mercaptan impurity, since it cannot be altered by caustic washing, and diallyl tetrasulfide which, because of its light yellow color, ready miscibility with mineral oil and very high sulfur content appeared very promising, was found to have a nauseating garlic odor. The few polysulfides in this group that do not possess such odors initially, almost without exception develop odors, upon use, that are or soon become so obnoxious as to cause machinists to walk off the job. In some instances the odors developed during use do not seem too unpleasant at first but for some reason become intolerable upon continued use due to a subtle accumulation of odors in high speed, automatic, multi-spindle machines, because of the large volumes of oil they require and the heat, violent agitation and splashing to which the oil is subjected. 7

,Proposals to utilize aryl sulfides in cutting oils relate generally to those aryl sulfides in which a sulfur atom or a chain of sulfur atoms is substituted directly on the aromatic nucleus. Thus, for example,'proposals have I been made to utilize aryl sulfides, such as phenyl-, tolyl-,

xylyl-, naphthyland anthracene sulfides in cutting oils without suggesting that there are any material differences among the many aryl sulfides that would make some of them less suitable than others.

It has also been proposed in the art to utilize in cutting oils aryl sulfides in which the sulfur atoms or chains of sulfur atoms are connected to the aromatic nuclei by meth-.

ene or ethene groups. These proposals are limited, however, to aryl sulfidies in which one methyl group and, in one unsupported, purely prophetic proposal, two methyl groups, are substituted on the aromatic nuclei, the number of sulfur atoms is limited to two despite generalizations as to polysulfides, and the number of aryl groups in the molecule is likewise limited to two. It appears to be generally believed in the art that in this more limited class of aryl sulfides, the monosulfides and disulfides are to be preferred over sulfides containing more vthan two sulfur atoms and the unsubstituted aryl sulfides are to be preferred over substituted aryl sulfides. This preference is apparently based on conclusions by some investigators.

that the lengthening of the sulfur chain and the substitution of alkyl groups on the aryl nuclei would both contribute to reducing the oil-solubility of such compounds and to making them solid rather than liquid at ordinary temperatures.

The surprising and unexpected discovery has now been made that it is feasible to prepare organic polysulfides of appreciably higher sulfur content and molecular Weight than has hitherto been considered possible. These compounds are characterized by the general formula 'RSt--RS1R in which the Rs stand for alkylsubstituted benzyl radicals having a total of up to ten, i. e., at least seven and preferably ten carbon atoms, R stands for an alkyl-substituted xylylene radical having a total of up to eleven, i. e., at least eight and preferably eleven carbon atoms, and x is at least 3 and preferably addition to lubricating oils in order to produce cutting oils. carbon polysulfides, when added to lubricating oils, form compositions having acceptable cutting abilitiesf Un-' fortunately, however, most of these hydrocarbon polysulfides, as such and when diluted or blended with a Thus, for example, diamyl tetrasulfide has an exceeding- Tests have shown that some of this class of hydro- 4 or 5. These di-polysulfides, and mixtures thereof with alkyl-substituted benzyl polysulfides are viscous materials, readily soluble in cutting oil bases, substantially odorless, transparent, light yellow in color, and have low volatility and excellent adherence to cutting surfaces at high temperature, all properties making them eminently suitable as cutting oil concentrates;

Generally, the method of the invention'comprises re 5 ';acting a mixture containing one or more alkyl-substituted 1y unpleasant odor that is characteristic of the polysulfide .sulfur at an elevated temperature.

benzyl monohalides and one or more alkyl-substituted xylylene dihalides, the benzyl halides and xylylene dihalides being present in a molal ratio greater than 2:1

with an excess of alkali-metal polysulfide and elemental The reactants may all be mixed together and reacted in a single step. It is" preferred, however, first to react a benzyl monohalidexylylene dihalide mixture with an alkali-metal polysulfide to form the corresponding xylylene di-polysulfides,, or a mixture thereof with alkyl-substituted benzyl polysulfides containing an average of at least about three and preferably about four sulfur atoms per sulfur bridge. These compounds and mixtures are highly useful as cutting oil concentrate but are then preferably reacted with elemental sulfur to form stable products containing an average of between about four and five, and preferably close to fivesulfur atoms per sulfur bridge.

In accordance with one embodiment of the method of the invention, preferred because of the ready availability of the starting material, a catalytic reformate containing primarily the various isomers of trimethylbenzene and methylethylbenzene, as Well as some propylbenzenes and less heavily substituted alkylbenzenes, is chloromethylated by any suitable means such as, for example, by reaction with formaldehyde, or a formaldehyde engendering material, and HCl in the form of hydrochloric acid, hydrogen chloride gas, or both for from about two to about seven hours at temperatures of the order of about 150 F. This reaction is advantageously carried out while stirring the reactants under a reflux and, after the reaction is complete, cooling the reaction mixture to room temperature, separating the two immiscible phases, washing the oily layer with water and separating the aqueous phase, washing the layer with sodium carbonate solution until the products are neutral, separating the layers, washing the products again with water and separating the layers, and finally drying the products with anhydrous calcium chloride. The organic reaction product thus obtained is essentially a mixture of alkyl-substituted xylylene dichlorides having a total of eleven carbon atoms, i. e., primarily the various isomers of trimethylxylylene dichloride (CH3)3CsH(CH2C1)2 as well as some methylethylxylylene dichloride CH3(C2H5)C5H2(CH2C1)2 and propylxylylene dichloride (C3H7)C6H3(CH2C1)2, and of alkyl-substituted benzyl monochlorides having a total of ten carbon atoms, i. e., primarily the various isomers of trimethylbenzyl monochloride CH3 sCeHaCHzCl as Well 'as some methylethylbenzyl monochloride CH3(C2H5)COH3CH2C1 and propylbenzyl monochloride (Cs'HUCsHtCHzCl.

Under the conditions described, the molal ratio of the benzyl monochlorides to the xylylene dichlorid'es is normally at least about 3:1. Lower ratios, e. g., 2.88:1, have however been obtained with the same starting material by using a considerable excess of HCl in the form of a gas in the chloromethylation.

The mixture of benzyl monochlorides and xylylene dichlorides obtained in "this manner, or "any combination of alkyl-substituted benzyl monohalides and Xylylene diha'lides preferably containing ten and eleven carbon atoms, respectively, from any other source, the monoand dichloride beingpresent in a molal ratio greater than 2:1 and preferably about 3:1, is then reacted at an elevated temperature of the order of about 200 F., for several hours with an excess of sodium tetrasulfide in the form of an aqueous solution. Upon cooling the reaction mixture to about 110 to 125 F. and settling, the reaction mixture forms an organic phase and an aqueous phase. The aqueous phase is separated and the remainder, i. e., the organic phase, is washed with alkali-metal hydroxide solution by stirring for about one-half hour atllO to 120 F. and, if desired,'treated witha mineral adsorbent. Upon separation of'the alkali hydroxide solution, whichforms a lower .1 layer, high yields are obtained of a composition comprisingprimarily di-polysulfides having the formula in which the Rs stand for alkyl-substituted benzyl radicals having ten carbon atoms, R stands for an alkylsubstituted xylylene radical having eleven carbon atoms, and x is an average of at least about 3 and generally about 4. For convenience, these compounds are referred to herein as the xylylene di-tetrasulfides or the trimers.

Tests have shown that when the benzyl monochlorides and xylylene dichlorides are present in the mixture reacted With sodium tetrasulfide in a ratio of 2:1 or less, the resulting products are insoluble in mineral cutting oil bases and presumably have a long chain, polymer structure. It is believed, therefore, that the monochlorides act as chain stoppers in avoiding the formation of such polymers and promoting the formation of trimers and that monochlorides in excess of the 2:1 molal ratio form the corresponding alkyl-substituted benzyl polysulfides or dimers, which act as diluents for the trimers. The. oil-soluble organic products of reaction with sodium tetrasulfide are probably mixtures of one or more of the described xylylene di-tetrasulfides with alkyl-substitutcd benzyl tetrasulfides. When the molal ratio of monochlorides to dichlorides reacted with sodium tetrasulfide is about 3:1, the molal ratio of the xylylene di-tetrasuliides to the benzyl tetrasulfides is about 2:1.

The reaction between the halides and alkali-metal polysulfide is preferably carried out in the presence of a diluent having a low viscosity and a high flash point. Hydrocarbon fractions having boiling points ranging from the kerosene to the fuel oil boiling ranges, generally designated as gas oil, are particularly suitable for this purpose. The addition of gas oil or fuel oil which does not react with either the reactants, the alkyl-substituted xylylene and benzyl tetrasulfides or the ultimately desired alkyl-substituted xylylene and benzyl pentasulfidcs, has the highly desirable and purely physical functions of imparting to the mixture thereof lower viscosities than either the tetrasulfides or the pentasulfides per se, facilitating the handling of the reactants and the products, and aiding in the separation of any aqueous phase after the reaction. Alkyl-substituted benzenes having boiling points above about 300 F., such as any that may be unreacted in the chloromethylation described, are, like the dimers, also eminently suitable as diluents. The diluent remains with the organic phase and serves as such in the succeeding reaction step with elemental sulfur.

The tetrasulfides obtained by reaction of the benzyl monochlorides and xylylene dichloridcs with sodium polysulfide are then reacted, preferably under an inert atmosphere such as nitrogen and while remaining in the presence of the diluent, with an excess, preferably about 5%, of elemental sulfur for two to three hours at a temperature between about 200 F. and about 300 F., preferably about 240 F., to form the corresponding pentasulfides, :so referred to herein because they contain an average of close to five sulfur atoms between adjacent aryl groups.

It ,is to be understood, of course, that it is within the scope of the invention to prepare any one or a selected combination of alkyl-substituted xylylene dipoly' sulfides of the general formula R--SeR-SR in which the Rs stand for alkyl-substituted benzyl radicals having a total ofup to ten, i. e., at least seven and preferably ten carbon atoms, R is an alkyl-substituted xylylene radical having a total of up ,to eleven, i. e., at least eight and preferably eleven carbon atoms, and x .is atleast 3 and preferably 4 to S, by appropriate selectiongof the corresponding starting materials, or by separation thereof from a mixture of polysulfidcs with the aid of a selective solvent such as 2-methyl-2,4-pentanediol, pentane, isopropanol, amyl alcohol, and the like. It

.' is also within the scope of the invention to prepare compositions containing such alkyl-substituted xylylene dipolysulfidezor polysulfides in combination'with anyone oi a selected combination of alkyl-substituted benzyl polysulfides.

Concentrates containing as little as about 10% or less alkyl-substituted xylylene di-polysulfide in alkyl-substituted benzyl polysulfide or hydrocarbon diluents such as gas oil, and containing as much as about 50 to 70% or more di-polysulfide in a hydrocarbon diluent, have superior cutting ability, transparency and excellent odor characteristics even without being blended with a cutting oil base. The polysulfide content of the concentrate may be entirely alkyl-substituted xylylene di-polysulfide or it may be an admixture of as little as about one mol of the dipolysulfide, i. e., the trimer, to nine mols of alkylsubstituted benzyl polysulfide, i. e., the dimer. Molal proportions of trimer to dimer in the ratio of about 2: 1, obtained by reacting alkyl-substituted benzyl monohalide and alkyl-substituted xylylene dihalide in proportions of about 3:1 with an alkali-metal polysulfide and elemental sulfur are preferred.

Both the tetraand pentasulfides of the invention, diluted or not with a suitable hydrocarbon diluent such as gas oil, and admixed or not with alkyl-substituted benzyl tetraor pentasulfides, may be blended to form stable and clear solutions with any mineral cutting oil base, preferably an acid-treated oil having a viscosity between about 75 and 300 SSU at 100 F., and said cutting oil base may itself contain free sulfur dissolved therein. The lower limit of viscosity specified is imposed largely by sulfur solubility. Oils having viscosities higher than 300 SSU at 100 F. are not preferred because of dificulties of handling and flowing. Cutting oil blends containing as little as 0.5% or less by weight of alkylsubsti-tuted xylylene di-tetrasulfide or di-pentasulfide have excellent cutting ability. The concentrates of the invention and the cutting oil blends containing the concentrates combine this unusually excellent cutting ability with low volatility, ability to stay on the tool and the work at the cutting point even at high temperature, absence of ob-v jection-able odor either upon standing or in severe use and ability to form stable blend with cutting oil bases. For cutting operations on ductile steels, sulfurized oil blends containing between about 0.5% and 5% by weight of the concentrate are highly satisfactory.

Perhaps the most surprising characteristic of the cutting oil concentrates of the invention is that they make it possible to incorporate into a cutting oil blend more active sulfur than is required or desired for some types of cutting operations. The present invention, therefore, provides an excellent means of controlling accurately the amount of active sulfur in a cutting oil so that it will be the optimum amount for any particular metal cutting operation. It is also possible to add small amounts of other ingredients, e. g., 1% by volume lard oil, that mask the effect of excess sulfur.

It is to be understood that while the products of this invention consist essentially of one or a combination of the named alkyl-substituted xylylene di-polysulfides, preferably diluted witth alkyl-substituted benzyl polysulfides or unsulfurized gas oil or both, and blended or not with a mineral cutting oil base, conventional additives such as lard oil, graphite, and oil soluble chlorinated compounds such as chlorinated wax and chlorinated aromatics typical of which is chlorinated biphenyl and the like may be added in amounts that do not materially alter the character of the products. It is also within the scope of the invention to add minor proportions, i. e.,

of the order of 1% or less, of antioxidants.

The blending of the cutting oil of the invention with lard oil in an appreciable amount, i. e., above about 1%, and preferably from about 2 to by volume, is particularly desirable and advantageous for reducing tool wear when cutting operations are carried out on abrasive steels and has the further advantage of providing a cutting oil that is most universally useful on both abrasive steels and ductile steels. One example of such a preferred cutting oil is a blend of a mineral cutting oil base with about 4% by volume of lard oil and about 1%- by weight of a 60/40 mixture of the xylylene polysulfide and gas oil. It is to be understood, therefore, that is is within the scope of the invention to add amounts of lard oil which do alter somewhat the character of the xylylene polysulfide-containing cutting oils of the invention in so far as the machining of abrasive steels is concerned.

The advantages and utility of the cutting oil concentrate, cutting oil and method of this invention will be-' come more apparent from the following example illustrating the invention.

EXAMPLE Part A 120 parts by weight of Solvesso 100, a catalytic reformate comprising a mixture of 4% aliphatic hydrocarbons and 96% aromatic hydrocarbons containing approximately 39% by weight trimethylbenzene isomers (7% 1,3,5-trimethylbenzene, 27% 1,2,4-trimethylbenzene,

and 5% 1,2,3-trimethylbenzene), 36% by weight methylethylbenzene isomers (20% l-methyl-3-ethylbenzene, 8% l-methyl-4-ethylbenzene, 8% 1-methyl-2-ethylbenzene), 3% isopropylbenzene and minor amounts of m-xylene (3%), o-xylene (6%), p-xylene (trace) and 13% unidentified monoalkylbenzenes probably including propylbenzene isomers, were refluxed at 140 to 158 F. for seven hours under a water condenser while stirring the reactants with 525 parts by weight of 36% aqueous hydrochloric acid and 42.8 parts by weight of 91% paraformaldehyde in the form of flakes. During the reaction a slow stream of HCl gas was fed to the reaction mixture and care was taken to provide good ventilation. After seven hours, the reaction mixture was cooled to room temperature and allowed to settle into two immiscible layers, the lower aqueous layer was separated, the upper oily layer was washed with water then washed with a 5% aqueous sodium carbonate solution until neutral and then washed again and finally dried with anhydrous calcium chloride.

56% by weight of the final oily phase was found to be a mixture of alkyl-substituted benzyl monochlorides, i. e., primarily trimethylbenzyl monochlorides and methylethylbenzyl monochlorides, 22% was found to be a mixture of alkyl-substituted xylylene dichlorides, i. e., primarily trimethyland methylethylxylylene dichlorides, which is approximately a 3:1 mol ratio, and the remaining 22% was found to be substantially unreacted.

Part B 162.2 parts by weight of the above-described approximately 3:1 molal mixture of benzyl monochlorides and Solvesso 100, were admixed with 244 parts by weight of a 40% aqueous solution of sodium tetrasulfide and with 152 part by weight of a gas oil having a viscosity of 42 SSU at F. and a flash point at 275 F. The mixture was subjected to reflux at 200 F. for about five to six hours while stirring well. The reaction mixture was then cooled to about 120 F. and allowed to settle, the lower aqueous phase was separated, the remaining organic phase was treated with about 20% by volume of a 3% aqueous sodium hydroxide solution and stirred for thirty minutes at 110-120 F., the caustic then being separated. Thereupon, 3% by weight Super Filtrol, a mineral absorbent, was added and the mixture stirred for about ten minutes at l10l20 F. The mixture was then filtered to yield 94 to 99% of the theoretical yield of a 46% concentrate, in the gas oil, of a mixture believed to comprise essentially polysulfides of the formulae R--S:cR'-Sa:R

and RS:rR in the ratio of about 2 to 1 mols, in which al havi a tot l of. slevensarbon at m and x averages about 4.

This concentrate was found, upon analysis, to have a total sulfur content of 14.0% and an active sulfur content of 7.1%, indicating that the sulfur bridges in the .polysulfide contains an average of approximately four sulfur atoms.

Part C 330 parts by weight of the 46% concentrate prepared in accordance with part B of the example were admixed with 12.85 parts by weight of sulfur and sufficient additional gas oil to maintain the ratio of polysulfide to gas oil at about 46/54. The mixture was then stirred for two hours under nitrogen atmosphere at a temperature of 240 F.

The yield of sulfurized concentrate was practically quantitative, the total sulfur content being 18.0% and the active sulfur content being 11.0%, indicating that the sulfur bridges in the polysulfide contain an average of about five sulfur atoms.

Part D A cutting oil base was prepared by adding to Diamond Paratiin oil, an acid-treated lubricating oil stock having a viscosity of 100 SSU at 100 F., 0.8% by weight elemental sulfur, i. e., the maximum amount of sulfur soluble in the oilat C. The mixture was heated and stirred at 200 'F. until all of the sulfur was dissolved. This took approximately one to two hours.

Blends of the cutting oil base with 0.5 to by weight of the 46/54 concentrate prepared in part B of the example and with 0.5 to 5% by weight of the 46/54 concentrate prepared in part C of the example form excellent cutting oils'characterized by remarkable cutting ability, low volatility and absence of odor, and ability to remain on the work and the tool at the point of cut.

A blend of the cutting oil base with 1% by volume of a 60/40 xylylene di-pentasulfide-gas oil concentrate, 4% lard oil and 0.5% Aroclcr 1254, a chlorinated biphenyl available as a yellow-tinted, viscous oil having a chlorine content of 54%, a specific gravity between 1.538 and 1.548 and a distillation range of 365390 C., said cutting oil having a total active sulfur content of approximately 0.9%, was tested in thread-cutting, chamfering, and cutoff operations.

In the thread-cutting operation, tie rods were made from C-1022 steel forgings. The finish was taken as the criterion of tool life, which was considered an end when either tearing of the thread flank and crest or chip welding at the root of the chaser land occurred. In these tests, as many as 2100 tie rods were threaded before tool failure.

In the chamfering and cut-oif operation, ductile (3-1010 steel was used. While the best cutting oil heretofore on the market gave a chamfering tool life of ten hours and a cutting tool life of seven hours, the cutting oil of the invention gave good operation for ten hours (the length of the test) with both tools and examination of the Work and tools at the end of the tests indicated that continuation of the tests beyond the ten hour period would have shown the tool life to be considerably longer than ten hours.

The product of the invention can also be prepared, with improved yield, by the method described in copending application Serial No. 455,748, filed September 13, 1954, now abandoned.

It is to be understood that various modifications of the method and products described herein will readily occur to those skilled in the an. All such modifications are intended to be included Within the scope of the invention as defined in the accompanying claims.

We claimi 1. A cutting oil concentrate comprising from about 50 to about 70% by weight of a mixture of organic dipolysulfides having the formula CiH5 CzHs

CrHti CH3 CH3 CH: where x averages between about 4 and 5, and from about 50 to about 30% by weight of a hydrocarbon diluent.

3. A cutting oil concentrate comprising from about 50 to about 70% by weight of a mixture of organic dipolysulfides having the formula R1 R: It:

and the formula where R1, R2 and Rs are selected from the group consisting of three methyl radicals, one methyl and one ethyl radical, and one propyl radical, and x is at least 3, and from about 50 to about 30% by weight of a hydrocarbon diluent.

4. A cutting oil concentrate comprising from about 50 to about 70% by weight of a mixture of organic dipolysulfides having the formulae ant-arcing) (CH3): H3):

CHr-S =-C1-I2 and the formulae Gout-spont- D op CH: CH;

@ctn-m-creQoma-omQ a a Rt OHz-Sg-CHT CHa CH;

where R1, R2 and R3 are selected from the group consisting of three methyl radicals, one methyl and one ethyl radical, and one propyl radical, and x averages at least about 3.

6. A cutting oil comprising a mineral oil containing up to about 0.8% free sulfur dissolved therein and from about 0.5 to about 5% by weight of a mixture of organic dipolysulfides having the formula @CHa-SrCHa-Q-CIHa-BrCHTQ R1 R2 R3 where R1, R2 and Rs are selected from the group consisting of three methyl radicals, one methyl and one ethyl radical, and one propyl radical, and x averages between about 4 and '5. v

7. A cutting oil comprising a mineral oil and from about 0.5 to about 5% by weight of a mixture of organic dipolysulfides having the formula R1 R: R3

and the formula QCHPSrOHrQ R1 Ra CHrSrCH CHrSs-OH R1 R: R:

and of benzyl polysulfides having the formula Q-CHPSFCHPQ where R1, R2 and Rs are selected from the group consist ing of three methyl radicals, one methyl and one ethyl radical, and one propyl radical, and x is at least aboutB, and the molal ratio of benzyl xylyl polysulfides to benzyl polysulfides being about 2:1.

References Cited in the file of this patent UNITED STATES PATENTS 2,273,471 Kimball Feb. 17, 1942 

5. A CUTTING OIL COMPRISING A MINERAL OIL AND FROM ABOUT 0.5 TO ABOUT 5% BY WEIGHT OF A MIXTURE OF ORGANIC DIPOLYSULFIDES HAVING THE FORMULA 